In mobile cellular telephony networks, voice connections are provided by Circuit Switched (CS) service and data connections are provided by Packet Switched (PS) service. User equipments (UEs) use different types of modems to connect to the network via different radio access technologies (RATs). For example, a modem can be operated in GSM (briefly 2G), WCDMA/CDMA2000/TDS-CDMA (briefly 3G), or WiMAX/LTE/TD-LTE (briefly 4G). If a UE is equipped with dual-standby capable modem, then the UE is able to access the network via different RATs.
Dual-SIM Dual-Standby (DSDS) is a very popular feature in smart phone markets today, especially in developing countries such as China and India. Many mobile phone users have multiple SIM cards for various purposes—having different phone numbers for different uses (e.g., one for business and one for personal), saving roaming fee, compensating non-contiguous network coverage, and sharing one device for multiple family members. With DSDS feature, mobile phone users can use single device to enjoy multiple SIM services. For DSDS UE, however, there is PS service continuity issue. The registration information of each SIM of a DSDS UE is independent in the network. When PS service is preempted by higher priority CS service, the PS path may be switched from a first modem to a second modem. As a result, it is not possible to reuse the same registration information after PS path switch because the IP address may change after PS path switch and result in the termination of the PS connection.
As an alternative to DSDS, some UEs may be equipped with dual-standby capable modem supporting a single SIM card. For example, a UE has a first modem that supports both PS and CS services and a second modem that supports only PS service. The UE may be configured to enter a standby mode for the two modems to listen to 2G/3G and 4G mobile terminated (MT) paging messages. The UE may also be configured to connect to the cellular network for PS or CS transceiving for only one of the modems at one time using shared RF resource, e.g., an antenna, a radio frequency (RF) module, or the combination thereof. The PS service could be interrupted when a CS connection is to be established, and MT CS paging messages can be listened while data transceiving of PS service is performed. Because the UE only has one SIM card, a SIM proxy may be implemented to read or write data from or to the SIM card for one of the modems. In addition, for sharing the RF resource, a radio frequency scheduler (RFS) is implemented to control the shared RF resource for data transceiving of one of the modems.
FIG. 1 (Prior Art) illustrates service control examples by a UE having single SIM card and dual-standby feature in a mobile communication network 100. The UE is equipped with a first modem supporting CS service and a second modem supporting PS service. In step 111, the UE establishes a mobile-originated (MO) CS connection via the first modem. During the MO CS call, the UE receives a paging message for PS service (step 112). Because CS call has higher priority over PS service, the UE rejects the PS service request (step 113). After the MO CS call is terminated, the UE receives another paging message for PS service (step 114). In step 115, the UE establishes a PS connection for PS service via the second modem. In step 116, the UE receives a paging message for MT CS service. Because CS call has higher priority over PS service, the UE establishes an MT CS connection in step 117 via the first modem and suspends the PS service. Upon completion of the MT CS call, the UE resumes the PS service in step 118 via the second modem. In step 119, the UE initiates an MO CS call and establishes an MO CS connection in step 120 via the first modem while suspending the PS service again. Upon completion of the MO CS call, the UE resumes the PS service in step 121 via the second modem. In step 122, the UE performs a CS location update (LU) procedure because of entering new location area. CS LU procedure also has higher priority over PS service. In step 123, the UE performs CS LU procedure via the first modem and suspend the PS service. Upon completion of the CS LU procedure, the UE resumes the PS service in step 124 via the second modem. It can be seen that the second modem may arrange PS data transceiving discontinuously, enable the first modem to listen to MT CS paging, initiate MO CS call, perform LU procedure, etc. with the aid of RFS.
In the Example of FIG. 1, the first modem supports only CS service, while the second modem supports only PS service. In some other scenarios, the first modem may allow both CS and PS services simultaneously. For example, a modem operating in 3G RAT allows both CS and PS service at the same time. Furthermore, the two modems may offer different data rate for PS service. For example, a modem operating in 4G RAT (e.g., LTE) can provide in excess of 100 Mbps peak data rate in DL and 50 Mbps in UL, which is much faster than 3G RAT. Therefore, for UEs with single SIM card and dual-standby feature, it is desirable to find a solution to fully utilize the different capabilities of the modems to maintain PS service continuity and provide higher PS data rate, while still guarantee the higher priority of CS service.